It’s just 15 inches south of your chin, and you can touch it while whistling and standing on one leg. But how well do you really know your belly button?

A paper published last week in the research journal PLOS One suggests just how alien an environment it might be. Scientists and citizen explorers working on the Belly Button Diversity Project, one of many projects run by Your Wild Life, an ongoing enterprise “exploring the ecological frontiers that exist right under our noses,” analyzed swabs from 66 people’s navels and found 2368 different bacteria species.

The paper, titled “A Jungle in There: Bacteria in Belly Buttons are Highly Diverse, but Predictable,” found that for all the differences from one navel to another, eight species stood out as the guests that wouldn’t leave. Termed “oligarchs,” they were present in more than 70 percent of individuals.

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As biologist Rob Dunn writes in Scientific American’s guest blog, there’s more work to be done:

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“While it is interesting to be able to predict which species of bacteria are frequent and/or abundant in belly buttons in general, what we cannot seem to account for is which species are present in any particular belly button, say that of [science writer] Carl Zimmer (who has written about his own hairy nub...). We would love to know what accounts for why I have a belly button dominated by one set of species and Carl Zimmer has a belly button dominated by another.”

If you’d rather think about smelly armpits, Your Wild Life’s Armpit-pa-looza project is in a pilot stage.

The hundred-year book project

Anybody familiar with math or physics likely knows the name Leonhard Euler. Euler, who died in 1783, was a giant who worked in a range of subjects from integral calculus to acoustics, from astronomy to music theory to shipbuilding. One of his best-known equations, Euler’s Identity, was once voted the most beautiful theorem in math.

Euler was astonishingly prolific, and the complete edition of his scientific works has become one of the most extraordinary projects in publishing. He produced more than 500 research papers and some two dozen books; when he died, he left behind about 300 more articles in manuscript form.

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When work began on the “Leonhardi Euleri Opera Omnia” in 1908, the committee overseeing its publication estimated the total number of volumes to come at 43. In 1913, that number was increased to 66, and shortly thereafter to 72. Now, after more than a century—and the deaths of various editors working on the “Opera”—the final two of the “Opera”’s now 74 volumes, on positional astronomy, are planned to be published by the German publisher Springer by 2014. (Euler addicts fearing withdrawal can rest easy: There is also a correspondence series underway.)

In addition to the pure quantity of material, publishing the work of an Enlightenment polymath poses certain challenges to modern scholars. In an e-mail to Brainiac, Martin Mattmüller, secretary of the Euler Committee based in Basel, Switzerland, wrote that “mathematicians and physicists with a sound knowledge of Latin are a threatened species (in Europe, too); and philologists or cultural historians without a specific interest in scientific issues rarely study texts of this kind (and I regret to have to say that when they do, there is often a considerable risk of mis-interpretation). So a competent transcription of 17th- or 18th-century texts dealing with issues in the exact sciences is not an easy task.”

A fir tree in C minor

If you’re an observant person, you may have noticed that the cross-section of a tree, with its concentric rings, looks a lot like a phonograph record. So...could you actually play it?

Someone has come up with a way. Inspired by Jethro Tull’s album “Songs From the Wood,” Austrian media artist Bartholomäus Traubeck created a record player that plays slices of wood, 12 inches across and 8 millimeters thick.

Tree rings can’t actually be played like a record—among other things, they’re concentric circles rather than the long spiral groove of an LP. Traubeck’s modified turntable uses a camera instead of a needle, turns the rings into data, and then uses an algorithm to translate it into piano “music.”

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“Sometimes it is a series of piano tones, sometimes it’s just one sound and the melody is defined, for instance, by the rate of growth,” Traubeck told PRI’s Living on Earth earlier this year.

“Whenever you put a fir tree on, you will get C minor, usually,” Traubeck said.

Elizabeth Manus is a writer living in New York City. She has been a book review editor at the Boston Phoenix and a columnist for The New York Observer and Metro. She maintains a blog, The Ys Have It, and is a member of the Literary Wing of the Lark Play Development Center.